1. Field of the Invention
The present invention relates to lead carriers such as a lead frame and a film carrier tape used for semiconductor integrated circuit (IC) devices.
2. Description of the Related Art
In the following description, lead frames used for typical semiconductor IC devices and film carrier tapes (often called "TAB tape") used for semiconductor IC devices fabricated by tape automated bonding (TAB) are generally referred to as "lead carriers."
In general, a film carrier tape, on which a liquid crystal display (LCD) driver chip is mounted, is provided with an input-side outer lead hole in which an input signal lead wire group is situated, a device hole in which the chip is situated, and an output-side outer lead hole in which an output signal lead wire group is situated. These holes are located in this order in the direction of tape feed. One end portion of the lead wire is electrically connected to the LCD driver chip. The other end portion of the lead wire serves as an input terminal of the chip in the case where the lead wire is one for input signals, or serves as an output terminal of the chip where it is one for output signals. The said one end portion is called "inner lead", and the other end portion is called "outer lead."
The number of input-signal lead wires of the LCD chip is 20 to 50, whereas the number of output-signal lead wires is 160 or more. The number of output-signal lead wires has been increasing more and more, with development of functions of devices. The problem is the increase in number of output-signal lead wires.
When lead wires are formed on a base film, a minimum wiring pitch is determined for the purpose of accuracy for processing. The minimum pitch between lead wires differs between the inner-lead side and the outer-lead side. In general, the pitch on the inner-lead side is small, and the pitch on the outer-lead side is large. Accordingly, the pitch between lead wires is small in the device hole, and it is large in the outer lead hole.
In order to form lead wires having different pitches between both-side portions thereof with an integrated conductor pattern, it is necessary to form the conductor pattern in a-fan-shaped manner on base film portions between the device hole and outer lead holes. For this purpose, a distance L is provided between the device hole and outer lead hole in accordance with the number of lead wires, thus keeping regions for forming the fan-shaped conductor pattern. However, if the number of lead wires increases, it is necessary to increase the area for forming the fan-shaped conductor pattern, i.e. the distance L between the device hole and outer lead hole.
The distance L increases substantially in proportion to the increase in number of lead wires. In other words, if only the number of output signal lines increases with the pitch unchanged, the distance L increases gradually.
If the distance L increases, the device region necessary for one device increases. As a result, the amount of film necessary for one device increases, and the yield of devices per film tape reel decreases. Thus, the manufacturing cost of devices increases.